Indirect air heater



May 14, 1940- H. L. GRAPP 2,200,549

INDIRECT AIR HEATER Filed April 4, 195s 2 sheets-sheet 1 1719.1 f5 ffwww May 14, 1940. H. GRAPP INDIRECT AIR HEATER Filed April 4, 1938 2Sheets-Sheet 2 I--- r- Il l rf MW pw .IVI n/.r JF f w f A T@ ma@indented May 14, 194() UNITED STATES PATENT ortica 2 Claims.

This invention relates to a heating device and particularly to such adevice for heating a gas such as air. More specifically the inventionrelates to what is known as an indirect heater.

Such heaters are used to heat air to quite a high temperature and thisheated air is used in various industrial drying and baking processes asin ovens where various objects have a coating dried thereon. Suchheaters may also be used for space w heating. The type of the inventionis that wherein the air is heated by a furnace which may use anysuitable fuel such as gas or oil.

It is an object of the present invention to provide such a heater ofsimple, highly eflicient and inexpensive construction, and which can beeasily assembled.

It is more specifically an object of the invention to provide such aheating device adapted to be disposed over a furnace and comprising acasing having extending vertically therethrough a plurality of rows offiat narrow tubes through which the products of combustion from saidfurnace pass, means being provided for circulating air between saidtubes in a circuitous path.

It is a further object of the invention to provide an indirect heatercomprising a casing adapted to be disposed over a furnace havingvertical side and end walls and novel top and bottom plates adapted toreceive and support a large number of tubes extending therebetweenthrough which products of combustion pass and between which the air tobe heated is circulated,

said tubes being arranged for convenient cleaning.

These and other objects and advantages of the invention-will be fullyset forth in the following description made in connection with theaccompanying drawings in which like reference characters refer tosimilar parts throughout the several views and in which:

Fig. 1 is a view in vertical section taken substantially on line i--l ofFig. 2;

Fig. 2 is a view partially in top plan and partially in horizontalsection taken substantially on 415 line 2--2 of Fig. 1; i

Fig. 3 is an end view of the heater as seen from the right of Fig. l;

Fig. 4 is a partial plan view of one of the tube holding plates, sometubes being shown in hori- 50 zontal section; f

Fig. 5 is a section taken on line 5-5 of Fig. 4 as indicated by thearrow; and

Fig. 6 is a partial perspective view of one of the j tubes used.

55 Referring to the drawings a device forming an indirect heater isillustrated, the same comprising a casing designated generally as l0which is adapted to be disposed above or over a furnace. In theembodiment of the invention illustrated a furnace is indicated havingend frames formed of vertical side angle members Il and transverselyextending angle members l2. A channel member I3 extends about the top ofthe furnace, vertical plates or wall members M being shown as disposedbetween angle members Il and l2 and the 1 channel i3. The furnace issupported by vertical channel members l5 extending to channel I3, whichsupport transverse angle members I6. Angle members i6 in turn supportlongitudinally extending bars l1 upon which are placed the brick I8forming the bottom of said furnace. Brick I9 form the end Walls of saidfurnace and extend between members i6 and channel members i3. Thefurnace may have an inner lining material 20 and the furnace chamber hastherein open brickwork 2l. Some suitable fuel burner such as an oil orgas burner will be disposed within said furnace, one end wall of whichwill be provided with a suitable opening la through which the burner orfuel supply conduit may extend.

The furnace described is one of somewhat usual construction and per seforms no part of the present invention. Casing l0 has a bottom plate mawhich has side and end portions resting upon the channel members i3. Atop plate lllb is provided which is a counterpart of plate I0 butreversely disposed and spaced above the latter a distance equalsubstantially to the height of casing il). Casing l0 has a frameextending thereabout at each end comprising the vertical angle members|00 and the top and bottom horizontal angle members ld. Spaced verticalplates ille extend across casing Hl and suitable insulating material 22is disposed therebetween. Casing l0 will also have suitable verticalside walls lf supported by the vertical angle members lc. Plates l0 andlb have on their adjacent faces a plurality of rows of recesses lng.These are shown as rectangular in form and are formed by transverselyextending projecting ribs Ih extending in parallel relation acrossplates Illa and lb and the spaced ribs lllz which extend between andjoin the ribs Ih. Within each recess log is a projecting oblong riblily' having closely adjacent parallel sides and semi-cylindrical ends,each of said ribs |07' defining anl opening lilla through its plate. Itwill be noted as shown in Figs. 2 and 4 that the ribs |051' are instaggered relation, said ribs in one row being disposed centrallybetween the ribs in the adjacent row. Plates Illa and |0b each have arib IUm extending thereabout atthe side opposite the ribs |07'. v Aplurality of tubes 23 extend between plates I 0 and I 0b and have theirends respectively fitting over the ribs |09' in said plates. Suitablesecuring material 24 such as a heat resisting or asbestos cement may bedisposed in the recesses |0g about the ends of tubes 23. Inner sideplates |09' extend between plates Ia and |0b having their lower portionssecured in an outer groove |0p by suitable cement. The tubes 23 may beof seamless or other convenient construction but in Fig. 6 a portion isshown made of one piece of metal bent into oblong form and having shortprojecting ribs 23a at one end of the tube which may be joined in anysuitable manner as by welding. A plurality of horizontal partitionforming plates 25 extend across casing I0 between the side walls IDf,said plates connecting with one end of casing I0. It will be noted thatalternate partitions 25 have their ends spaced some distance fromopposite ends of casing I0. Small curved plates 25a. are disposed at theends of plates 25 engaging the end walls of the casing, one of saidplates also being disposed at the lower rear corner of casing IU. An airinlet conduit 26 extends through the front end wall of said casing andthus through the plates Ille, the bottom of which is substantiallyaligned with the uppermost partition 25. An outlet conduit 21 alsoextends through the front end wall of said casing, the top of which issubstantially aligned with the lowermost partition 25. As shown in Fig.3 conduits 26 and 21 extend substantially the full width of casing |0. Avent hood 28 illustrated as made from sheet metal extends over the topof plate Illb so as to enclose all of the openings IUk, the same havingflanges secured to plate |01) by the screws 29. Said hood is providedwith a suitable opening at its rear end for the outlet of the gases ofcombustion and the same is shown as having a handle 30 on the topthereof. A plate 3| may be secured at each side of casing l0 extendingthroughout the length and heighththereof spaced therefrom and havingflanges at its edges secured by screws 32 to angle members |0d. Suitableinsulating material 33 may be disposed between plate 3| and the sides ofcasing l0.

In operation the furnace comprising members I to 2| will be suitably redand the hot products of combustion will pass upward therefrom throughthe tubes 23. These products of combustion will pass into the vent hood28 and will be led therefrom through a suitable conduit. Air will beblown into inlet conduit 2B and will pass into casing l0 and between thetubes 23 above the uppermost partition 25 to the rear end of the casingand will return below said partition and above the next adjacentpartition 25 to the front end of casing I0 when it will again traveltoward the rear end of casing I0 between tubes 23 above the lowermostpartition 25 and will then return below said lowermost partition to andthrough a discharge conduit 21. 'Ihe air will be directed by conduit 21to the desired point of use.

It will be noted that the air cannot take a straight path through thecasing IIJ between tubes 23 but must change its course at each row oftubes due to the staggered relation of said tubes. The tubes have alarge contact surface for the air and the air is quickly heated to ahigh degree by travelling in contact with said tubes, said air beingheated both by radiation and convection. It will be noted that the airnearest the outlet conduit 21 encounters the hottest part of the tubesor the part which is heated by the hottest products of combustion. Asstated, the large area of surface on the tubes and the arrangementthereof results in an eicient heating of said tubes and a very efficientheating of air travelling thereabout.

From the above description it will be seen that I have provided anextremely efficient heating device and one that is quite simple inconstruction. The device is compact and the space within the casing Illis used to maximum eiliciency. The tubes are simple in form and areeasily made and assembled. An important feature of the heater is thatthe tubes can be very easily cleaned. By removing the vent hood 28 whichis easily done, a cleaning device can be moved vertically down throughthe tubes and the tubes thus cleaned of any deposit. The inner sides ofthe tubes are unobstructed and the cleaning can thus be easily andquickly accomplished.

The header plates |0a and lb are made of a cast alloy having appreciablepercentages of chromium and nickel. In practice the plates have beenfound to `be very satisfactory when containing 11/2 percentage each ofchromium and nickel. The cast plates are quite durable and do not tendto grow, that is to permanently expand and crack as a result of hightemperature. The non-metallic packing or securing material 24 makes foreasy assembly of the device and for quick and convenient removal of atube should this be necessary.

The device has been amply demonstrated in actual practice, found to bevery successful and eflicient and is being commercially made.

It will, of course, be understood that various changes may be made inthe form, details, arrangement and proportions of the parts, withoutdeparting from the scope of applicants invention, which generallystated, consists in a device capable of carrying out the objects aboveset forth, in the parts and combinations of parts disclosed and dened inthe appended claims.

What is claimed is:

1. An indirect heating device adapted to be disposed over a source ofhot gases of combustion having in combination, a casing having top andbottom plates, a plurality of rows of tubes extending between said topand bottom plates, said tubes having at parallel sides, said plateshaving openings therethrough alned with the openings in said tubes andhaving grooves extending about said openings therein in which the endsof said tubes are disposed and high temperature resisting material insaid grooves about said tubes for holding the same in place whereby theends of said tubes are protected from the hot gases passing therethroughand means for passing air longitudinally through said casing about saidtubes.

2. An indirect heating device adapted to be disposed over a furnacehaving in combination, a casing having insulated vertical side and endwalls and a bottom plate overlying said furnace, a plurality of rows oftubes extending from said bottom plate, said tubes having flat parallelsides and being very elongated in horizontal cross section, said tubeshaving their sides extending lengthwise of said casing, the sides ofadjacent tubes being in close proximity, said bottom member havingopenings therethrough with which said tubes aline so that the hotproducts of combustion from said furnace rise through all of said tubes,a top plate over said tubes having openings with which said tubes aline,the ends of said tubes being disposed in said top and bottom 75 platesrespectively, an inlet conduit extending into said casing adjacent saidtop plate, a plate extending horizontally from the bottom of saidconduit around said tubes to the opposite end of said casing, an outletconduit at the end of said casing below said inlet conduit and adjacentsaid bottom plate, a plate alined substantially with the top of saidoutlet conduit extending horizontally about said tubes to the oppositeend of said casing and a plate extending from the end of said casingopposite said conduits around said tubes to adjacent the end of saidcasing with which said conduits connect whereby air entering said inletwill pass around said plates and said tubes to said outlet conduit.HERBERT L. GRAPP.

